如果我实现一个Iterator类来封装PDOStatement，key（）方法应该怎么做

Question

I developed a interface and class to shield the PDOStatement.

The interface:

interface ResultSetInterface extends Iterator
{
    public function count();
    public function all();
}

The class:

class ResultSet implements ResultSetInterface
{
    /**
     * @var PDOStatement
     */
    protected $pdoStatement;

    protected $cursor = 0;

    protected $current = null;

    private $count = null;

    public function __construct($pdoStatement)
    {
        $this->pdoStatement= $pdoStatement;
        $this->count = $this->pdoStatement->rowCount();
    }

    public function rewind()
    {
        if ($this->cursor > 0) {
            throw new Exception('Rewind is not possible');
        }
        $this->next();
    }

    public function valid()
    {
        return $this->cursor <= $this->count;
    }

    public function next()
    {
        $this->current = $this->pdoStatement->fetch();
        $this->cursor++;
    }

    public function current()
    {
        return $this->current;
    }

    public function key()
    {
    }

    public function count()
    {
        return $this->count;
    }

    public function all() {
        $this->cursor = $this->count();
        return $this->pdoStatement->fetchAll();
    }
}

This works fine. But I'm not sure how to use the key() method which is necessary to implement an Iterator class. Any ideas?

Answer 1

First of all, about your interface, I think it would be better for you to extend CountableIterator as you want to add the count()method and there is a magical interface for that purpose in SPL.

About the key method. You have to remember in PHP every iterable content is an association of a key and a value. It is inherited from PHP arrays.

Iterator is a way to overload the foreachoperator and as foreach as a sythax which is composed as foreach($iterator as $key=>$value) you have to give the key method implementation.

In your case you have two solutions :

• using the $pdo->cursor
• create your own attribute called $currentKey and increment it each time you use nextmethod.